FIELD OF THE INVENTION
The present invention relates to an input port fault diagnosing device which determines the proper operation or abnormal operation of an input port receiving detection signals from sensors and the like so as to determine whether or not said input port has faulted, and further relates to an output port fault diagnosing device which determines the proper operation or abnormal operation of an output port transmitting control signals under load so as to determine whether or not said output port has faulted.